Multiple susceptibility (Idd) genes contribute to T cell mediated autoimmune type 1 diabetes (T1D) in both humans and NOD mice, but with particular MHC haplotypes providing the primary risk factor. While also present in many non-autoimmune prone strains, the H2g7 MHC haplotype encoded Kd and/or Db class I molecules play an essential diabetogenic role when expressed in NOD mice. The overall goal of this project continues to be determination of the immunogenetic basis for the aberrant generation of diabetogenic MHC class I dependent CD8 T cells in NOD mice, with the hope such knowledge could ultimately provide translational information for blocking development of similar effectors in humans at high future disease risk. In NOD mice the H2g7 class I gene products aberrantly lose ability to mediate the intrathymic negative selection of diabetogenic CD8 T cells. A currently unknown polymorphic gene(s) within the Idd7 locus plays a major interactive role in determining whether H2g7 class I restricted diabetogenic CD8 T cells undergo negative selection. Hence, specific aim 1 is to more finely map, functionally characterize, and potentially identify the Idd7 region gene(s) regulating the negative selection efficiency of diabetogenic CD8 T cells. There is now also compelling evidence in humans that when expressed in the right genetic context, certain quite common MHC class I variants, such as HLA-A2.1, aberrantly contribute to T1D development. Supporting this situation is our finding that NOD. 2mnull.HHD mice expressing human HLA-A2.1, but no murine MHC class I molecules, continue to develop T1D. This was not a generic function of any human class I variant transgenically expressed in NOD mice. Previous work identified a series of pancreatic cell derived peptides that are presented by HLA-A2.1 class I molecules to diabetogenic CD8 T cells in NOD. 2mnull.HHD mice. T1D protective tolerance can be induced to pancreatic cell peptides that are presented by H2g7 class I molecules in standard NOD mice through appropriated dosed injections into young pre-disease state recipients. Diabetogenic CD8 T cells in standard NOD mice also undergo negative selection if forced to mature in the presence of engrafted antigen presenting cells (APC) expressing some non-H2g7 MHC haplotypes. Specific aim 2 will determine if diabetogenic HLA-A2.1 restricted T cell responses in NOD. 2mnull.HHD mice can be attenuated by a potentially tolerogenic peptide administration or APC engraftment protocol. In the currently available NOD. 2mnull.HHD stock only murine T cell receptor (TCR) molecules can engage antigens presented by the human HLA-A2.1 class I variant. Because of their respective human or murine origin, the TCR molecules expressed by diabetogenic HLA-A2.1 restricted T cells in T1D patients and NOD.2mnull.HHD mice might vary in their antigen binding affinities, which in turn could result in differential selection and/or activation effects. Thus, specific aim 3 is to functionally characterize NOD.22mnull.HHD mice transgenically expressing a human T1D patient derived TCR that recognizes a known HLA-A2.1 restricted pancreatic ss cell autoantigen.